Browser tests

+ new grunt task `mocha-test` that will run tests using phantomjs.
+ new grunt task 'server` that will start local server up
   (you can then open http://localhost:8000/spec to run unit tests
   in your browser).
+ new grunt task `watch` to watch file changes and run build again.
+ changed tokenizer tests: `match_tokens` and `be_token` are
   separate functions now to avoid `node` vs. `browser` vs. `phantomjs`
   shenanigans.
+ moved tests files to `tests` folder to avoid adding `script` tag for each
   new test (using `concat` task to put them all together).

/cc @wycats @kpdecker